Area and isolation predict metapopulation genetic structure of a pond-breeding amphibian

Background/Question/Methods

In metapopulations with demographic turnover, theory predicts that founder effects have an important role in determining spatial genetic structure.  However, among-patch heterogeneity in ecological factors (e.g., area, isolation, habitat quality) that affect extinction and colonization probabilities may also create spatial variation in the strength of genetic drift and gene flow, obscuring genetic founder effects.  We used microsatellite markers to test the hypothesis that ecological factors underlying extinction-colonization dynamics influenced the spatial genetic structure of a tiger salamander (Ambystoma tigrinum) metapopulation.  Our previous research demonstrated that occupancy dynamics of A. tigrinum in a complex of 41 wetlands were influenced by metapopulation factors (wetland area, spatial connectivity) and local habitat factors (predatory fish presence, wetland hydroperiod).  We used a hierarchical Bayesian approach to evaluate how population age (newly-colonized vs. established) and both metapopulation and habitat factors influenced the degree of genetic divergence among populations.  

Results/Conclusions

Newly-colonized populations were more differentiated than established populations, suggesting founder effects had a role in generating population genetic structure.  However, ecological variables related to metapopulation dynamics were more important than age in predicting genetic divergence.  Genetic divergence decreased with wetland area and spatial connectivity, indicating metapopulation factors had significant roles in generating spatial genetic structure.  Genetic divergence was not strongly related to fish presence or wetland hydroperiod.  This is one of the few studies to apply the area-isolation and habitat paradigms of metapopulation ecology to understand metapopulation genetic structure.  Overall, our results demonstrate that ecological factors driving metapopulation dynamics can be key predictors of spatial genetic structure, and that habitat area and isolation may mediate the contributions of gene flow and migration in shaping patterns of genetic divergence in a metapopulation.